(1) Field of the Invention
The present invention relates to an optical disc from and into which a read and a write can be performed and recording and reproducing methods to record and reproduce data on the optical disc. More specifically, the present invention relates to an optical disc on which video data is recorded, and recording and reproducing methods used for such optical disc.
(2) Description of the Related Art
DVD-RAM (Digital Video Disc-Random Access Memory) has been recently developed in the field of rewritable optical discs. A DVD-RAM is a phase change optical disc with a several-GB capacity that exceeds the conventional limits of around 650 MB.
DVD-RAMs can be used by computers to store various kinds of data. In addition, there are hopes that DVD-RAMs will be used to record AV (audio video) data for audio and video. While common conventional recording devices such as video tape recorders (VTRs) record audio and video onto a magnetic tape, there are hopes that such recording will be performed by optical disc recorders that use optical discs.
An optical disc recorder/player that can be used in place of a standard VTR receives a TV (television) broadcast, converts (compresses) a TV signal in the received broadcast into digital AV data, and records the digital AV data onto a DVD-RAM. When reproducing the AV data, the optical disc recorder/player reads the AV data from the DVD-RAM, converts the read AV data into an analog AV signal, and outputs it to a display unit. The generated AV data conforms to MPEG (Motion Picture Expert Group) prescribed in ISO/IEC 13818 (International Standardization Organization/International Electrotechnical Commission).
With some recent analog TV broadcasts, digital data is multiplexed into a TV signal during a vertical blanking interval (hereafter called "VBI", with the digital data multiplexed during a VBI being called "VBI data"). In teletext broadcasting, for instance, text data is multiplexed as VBI data during VBIs.
In a TV (or video) signal conforming to NTSC (National Television System Committee) system, one frame (i.e., two fields) is composed of 525 horizontal scanning lines, and VBI data can be multiplexed during a period that corresponds to the tenth to twenty-first horizontal scanning lines during a VBI and a period that corresponds to the 273rd to the 284th scanning lines during a VBI.
In addition to text data, VBI data can be information such as letterbox control information and copy control information. The letterbox control information is used to control display of an image with an aspect ratio of 4:3 on a display screen with an aspect ratio of 16:9 or 14:9. The copy control information shows whether VTRs are permitted to record the images. A method to multiplex such information as VBI data is defined, for instance, in Journal of the Institute of Television Engineers of Japan vol. 49 No. 9 (1995), and ETS300 294 (European Telecommunications Standards) "Television Systems 625-Line Television Wide ScreenSignaling (WSS)".
The letterbox control information and the copy control information are multiplexed into a program or a commercial. As the VBI data can be multiplexed into each field, it is possible to change, for instance, display and copy protection settings only for a certain commercial by multiplexing VBI data into the certain commercial. More specifically, it is possible to change an aspect ratio of a display image and/or allow copying only for commercials by multiplexing appropriate VBI data during the commercial periods.
VTRs for S-VHS (Super Video Home System) are capable of recording a TV signal including VBI data onto a magnetic tape, reproducing the TV signal, and having the TV signal displayed on a display unit. This allows the display unit to recognize the multiplexed VBI data such as letterbox control information and to control the displaying of a letterbox image in synchronization with the TV signal.
However, when a conventional optical disc recorder/player receives the TV broadcast, encodes an analog TV signal in the broadcast into compressed digital data, and records the compressed data onto an optical disc, any VBI data in the TV signal will be lost. As a result, the conventional optical disc recorder/player cannot change the display style or copying permission during fifteen or thirty-second commercial periods when reproducing AV data from an optical disc.